The effect of tetrandrine (518343) (TD) on enhancing the actions of the mutagens mitomycin-C (50077) (MMC) and cigarette smoke condensate (CSC) were examined. Chinese-hamster cell lines were exposed for 3 hours to: 20 microliters CSC; 40 or 80 micrograms/milliliter (microg/ml) TD; or 20, 40, or 80 microliters TD plus 20 microliters CSC without S9 activation. The cells were also exposed to 0.01microg/ml MMC; 40 or 80microg/ml TD; or 20, 40, or 80microg/ml TD plus 0.01microg/ml MMC. SCE scores of the individual compounds were compared with those of the combined treatments. CSC and MMC caused an increase in the frequency of SCEs, as did 80microg/ml TD after metabolic activation of the cells. Compared to the sum of the effects of CSC and TD alone, the combined effect of CSC plus 40microg/ml or more TD showed a 50% increase in SCEs. A similar enhancing effect was seen for MMC plus TD. The authors conclude that TD is an effective enhancer of the genotoxic actions of MMC and CSC.